Officials stopped short of ordering evacuations following the so-called strombolian eruption, explosions that consist of relatively mild blasts but eject burning cinders and lava bombs.
One of the Central American country's most active volcanoes, Pacaya began to expel lava at dawn, creating an immense column of smoke, video footage from the institute showed.
"The Pacaya volcano has a very high level of activity, which has generated a strombolian type eruption, with strong explosions," the meteorological institute, Insivumeh, said in a statement.
Comment: Guatemala: There's nowhere to hide - hundreds of thousands live in the shadow of 3 erupting volcanoes